Thursday, October 17, 2013

Asexual Reproduction in Plants

A few members asked us to post the presentation about asexual reproduction, so here it is. 

Unlike humans, plants can reproduce sexually and asexually. The advantages of asexual reproduction are that it is faster, less energy-consuming, and that it produces clones of the original plant - identical at a genomic level. However, it fails to increase diversity, and any susceptibility to disease that the original plant had will be passed on to its clones.

The simplest method of asexual reproduction is through cuttings. Cut a branch off of a plant (usually an herb) that is still soft and not woody yet, remove the lower leaves, and plant it in moist soil, adding rooting hormone if desired. That branch has the potential to develop into an identical plant. This normally happens in nature when branches of a plant are broken and fall down into soil; if the branches fall into an ideal environment with the right orientation, they can continue growing and form a new plant.

Layering is a similar technique, where part of the branch of the plant is buried beneath the soil or comes in contact with the soil. The submerged part of the branch will grow roots, and soon enough that branch will be able to obtain its own water and nutrients independent of the original plant; the branch can be severed and will develop into a mature clone.

A plant’s amazing ability to regrow from almost any part is due to the fact that the shoots and roots of most plants exhibit indeterminate growth, meaning that they grow continually, and even when separated from the original plant, can still grow to form a new plant.

Some plants send out stolons or runners, aerial stems that contain plantlets (miniature plants) capable of growing roots and developing into mature clones. Examples are strawberries and spider plants.

Rhizomes are the underground equivalent of stolons. Ginger and bamboo use rhizomes to expand, explaining why many people who grow bamboo for the first time have trouble keeping its growth under control.

Suckers are almost the same as rhizomes, except that they are much shorter (usually within a foot of the 
mother plant). A new plant arises with its roots intertwined with its parent’s roots. It’s a great way to get lots of clones of a plant fast. Examples are aloe vera, snake plant, and banana palm.

Certain succulents produce plantlets at the tips of their leaves, each of which is able to form a new plant. A prominent example is the Mother of Thousands plant.

Plants with bulbs or tubers can divide their respective systems to generate clones. Daffodils, tulips and garlic all have bulbs while potatoes have tubers.

More advanced techniques include grafting and tissue cultures. We won’t go too much in detail for these, but grafting involves joining two different plants together to obtain the best of their qualities; the bottom ‘rootstock’ provides a strong root system while the top ‘scion’ grafted to the rootstock has the growing and fruiting capabilities. The rootstock is cut and the scion is attached to the cut part, where the vascular systems combine to become one. It’s the fastest way to produce cultivars of fruit trees with the desired properties.

With tissue culture, you need small pieces of leaf from the plant you want to clone. These pieces are placed on sterile agar jelly with nutrients and hormones. With luck, the pieces will develop into small plantlets that can be transferred into regular media and grown like ordinary plants.


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